An optical receptacle is used as a component for optically connecting an optical fiber connector to an optical element such as a light receiving element, a light emitting element, etc., in an optical module of an optical communication transceiver (e.g., referring to Patent Citation 1).
In recent years, it is necessary to increase the speed of optical communication transceivers as IP traffic increases. Generally, the configurations of the transceiver and the like that employ the receptacle-type optical module are standardized; and it is necessary to downsize the optical module because the space necessary for the electronic circuit increases as the modulation rate of the optical signal emitted from a semiconductor laser which is one optical element is increased.
The mode field diameter of the semiconductor laser element is smaller than a core diameter of 10 μm of the optical fiber generally used as the transmission line of the optical signal.
In recent years, optical modules also are being used to increase the communication speed of optical transceivers, where the optical module has a structure in which multiple semiconductor lasers are included inside a single module; the light that is emitted from each of the semiconductor lasers is multiplexed in one waveguide inside the optical waveguide formed in the interior of a plate-like member; and subsequently, optical coupling is made to the optical fiber of the optical receptacle. To downsize these optical modules, it is necessary to downsize the plate-like member having the optical waveguide described above; and there is a trend of the core diameter of the optical waveguide becoming smaller.
In an optical module in which a light receiving element is used instead of the light emitting element as well, there is a trend of reducing the light-receiving diameter of the light receiving element for use in higher-speed longer-distance communication applications.
In the case where there is a difference between the fiber core diameter and the mode field diameter of the optical element, while it is necessary for the lens to have a magnification function to condense the light emitted from the semiconductor laser elements into the fiber core or condense the light emitted from the fiber core into the light receiving element, a method is known to prevent the module total length from simultaneously becoming undesirably long by reducing the fiber core diameter of a portion of the optical element side end surface of the optical fiber (e.g., referring to Patent Citation 2).
However, as in FIG. 1 or FIG. 2 of Patent Citation 2, normally, although it is necessary to locally add a refractive index control additive to the fiber to convert the core diameter while the outer diameter of the normal fiber remains constant, in this method, there is a problem of economic production being extremely difficult not only because the work method is complex but also because the control items are extremely numerous.
Also, unlike the description recited above, although it is possible to produce economically in the case where the outer diameter of the fiber tip changes and the core diameter of the tip portion changes as in FIG. 3, there is a problem of the fiber breaking and many cracks occurring because the portion that is exposed outside the ferrule has a lower strength due to the smaller outer diameter of the fiber due to the changing core diameter of the fiber end surface.